A light-sensitive material which comprises a support and a light-sensitive layer containing silver halide, a reducing agent and a polymerizable compound can be used in an image forming method in which a latent image of silver halide is formed, and then the polymerizable compound is polymerized to form the corresponding image.
Examples of said image forming methods are described in Japanese Patent Publication Nos. 45(1970)-11149 (corresponding to U.S. Pat. No. 3,697,275), 47(1972)-20741 (corresponding to U.S. Pat. No. 3,687,667) and 49(1974)-10697, and Japanese Patent Provisional Publication Nos. 57(1982)-13862, 57(1982)-142638, 57(1982)176033, 57(1982)-211146 (corresponding to U.S. Pat. No. 4,557,997), 58(1983)-107529 (corresponding to U.S. Pat. No. 4,560,637), 58(1983)-121031 (corresponding to U.S. Pat. No. 4,547,450) and 58(1983)-169143. In these image forming methods, when the exposed silver halide is developed using a developing solution, the polymerizable compound is induced to polymerize in the presence of a reducing agent (which is oxidized) to form a polymer image. Thus, these methods need a wet development process employing a developing solution. Therefore the process takes a relatively long time for the operation.
An improved image forming method employing a dry process is described in Japanese Patent Provisional Publications Nos. 61(1986)-69062 and 61(1986)-73145 (the contents of both publications are described in U.S. Pat. No. 4,629,676 and European Patent Provisional Publication No. 0174634A2). In this image forming method, a recording material (i.e., light-sensitive material) comprising a light-sensitive layer containing a light-sensitive silver salt (i.e., silver halide), a reducing agent, a cross-linkable compound (i.e., polymerizable compound) and a binder provided on a support is imagewise exposed to form a latent image, and then the material is heated to polymerize within the area where the latent image of the silver halide has been formed.
The above-mentioned image forming methods are based on the principle in which the polymerizable compound is polymerized within the area where a latent image of the silver halide has been formed.
Japanese Patent Provisional Publication No. 61(1986)-260241 describes another image forming method in which the polymerizable compound within the area where a latent image of the silver halide has not been formed is polymerized. In this method, when the material is heated, the reducing agent functions as polymerization inhibitor within the area where a latent image of the silver halide has been formed, and the polymerizable compound within the other area is polymerized.
Japanese Patent Provisional Publication No. 61(1986)-275742 describes an embodiment of the lightsensitive material, in which the silver halide, reducing agent and polymerizable compound are contained in microcapsules which are dispersed in the light-sensitive layer. The light-sensitive material employing the microcapsules (referred to as "light-sensitive microcapsules" hereinafter) can give a clear image improved in sharpness.
The polymerization reaction in the above-mentioned image forming method smoothly proceeds under alkaline conditions. Therefore, a base or base precursor is preferably contained in the light-sensitive layer. Examples of the base and base precursor are described in Japanese Patent Provisional Publications No. 61(1986)69062, No. 61(1986)-73145 and 62(1987)-264041.
In order to accelerate the polymerization reaction using the base or base precursor, the base or base precursor is preferably contained in light-sensitive microcapsules. However, if the base is contained in the light-sensitive microcapsules, the sensitivity of the light-sensitive material tends to decrease or the material tends to be fogged in the course of the storage. Japanese Patent Provisional Publication No. 62(1987)264041 discloses various base precursors. However, the base precursor is not stable during storage, or is not quickly decomposed to form a base when it is heated.
Further, there has been scarecely found a base precursor which is stable for a reaction condition (especially, reaction temperature ususaly in the range of 30.degree. to 80.degree. C.) in preparation of the shell of the lightsensitive microcapsules and quickly forms a base in a heat development process (heating temperature is ususally in the range of 80.degree. to 200.degree. C., which is generally 50.degree. to 120.degree. C. higher than the reaction temperature).
Therefore, the base or base precursor has been arranged outside of light-sensitive microcapsules in the light-sensitive layer as described in Japanese Patent Provisional Publication No. 62(1987)-209523. The base or base precursor permeates the light-sensitive microcapsules in a heat development process.